some methods are explaining in the slides like pH meter, paper indicators

1. Measurement of pH
15BS(CHEM)001

2. Introduction of pH
• The concept of pH was first introduced by the Danish chemist Peder
Lauritz Sorensen at the Carlsberg Laboratory in 1909. the notation
had the "H" as a subscript to the lowercase "p", as so: pH.
• The exact meaning of the "p" in "pH" is disputed, but according to the
Carlsberg Foundation, pH stands for "power of hydrogen".
• It has also been suggested that the "p" stands for the German Potenz
(meaning "power").

3. Definition of pH
• It is defined as the negative of the base-10 logarithm (log) of the H+
concentration.
• A knowledge of the concentration of hydrogen ions (more specifically
hydronium ions) is of the greatest importance in chemistry. Hydrogen
ion concentrations are typically quite small numbers.
• Therefore, chemists report the hydrogen ion concentration of a
solution in terms of pH.
• Mathematically it may be expressed as
OR

4. Cont….
• The pH concept is very convenient for expressing hydrogen ion
concentration. It was introduced by Sorensen in 1909. It is now used
as a general way of expressing other quantities also, for example,

5. MEASUREMENT OF pH
A) pH indicator:
• Using indicators, qualitative determinations can be made with
universal indicators that have broad colour variability over a wide pH
range and quantitative determinations can be made using indicators
that have strong colour variability over a small pH range.
• by using pH paper, indicator paper that turns colour corresponding to
a pH on a colour key. pH paper is usually small strips of paper (or a
continuous tape that can be torn) that has been soaked in an
indicator solution, and is used for approximations.

6. pH paper indicator:

7. pH measurement:
• pH meter
• The pH of a given solution can be measured with the help of an
apparatus called pH meter. This consists of a voltammeter connected
to two electrodes.
• (a) a standard electrode of known potential;
and
• (b) a special electrode(the probe) enclosed in a glass membrane that
allows migration of H+ ions. The glass case contains a reference
solution of dilute HCl.

8. Cont….
• The two electrodes are dipped in the solution to be tested. If this solution has a
different pH from the solution in the probe, an electrical potential results.
• Thus the potential between the standard electrode and the glass electrode varies
with the pH of the solution under test.
• This potential is recorded by an
inbuilt potentiometer of the pH meter.
• The potentiometer reading is
automatically converted electrically
to a direct reading of the pH of the
unknown solution.
• Knowing the pH of the
solution its hydrogen ion
concentration can be calculated

9. pH meter

10. pH Scale
• The scale on which pH values are computed is called the pH scale.
• The hydrogen ion concentration of different acidic solutions were
determined experimentally.
• These were converted to pH values using the above relations.
• Then these pH values were computed on a scale taking water as the
reference substance.
• We are add some water in the solution When the concentrations of H+ and
OH– ions in water are expressed in mole per litre, the value of Kw found
experimentally is 1.0 × 10– 14.
• it is obvious that one molecule of water dissociates to give one H+ ion and
one OH– ion.
• This means that the concentration
of H+ and OH– Ions in pure water is equal.

12. Problems:
The hydrogen ion concentration of a fruit juice is 3.3 × 10– 2 M. What is
the pH of the juice ? Is it acidic or basic ?
Solution:

13. Calculating OH–from pH
• If a solution has a pH of 5.50 at 25°C, calculate its [OH–].
• Solution:

14. Applications (is base on acidity or basicity
• pH in nature
• pH in soil
• Acid rain

15. Acid rain
• Acid Rain, form of air pollution in which airborne acids produced by
electric utility plants and other sources fall to Earth in distant regions.
Sulphur dioxide and nitrogen oxides react with water and other
chemicals in the air to form sulphuric acid, nitric acid, and other
pollutants. travel with the wind for hundreds of miles, and eventually
return to the ground by way of rain, snow, or fog, and as invisible
“dry” forms.